I believe that link juice is meant as an expression of how much of a Page's PR is transferred by a link.
This will vary according to the number of OBL on the page etc.
Bing (yahoo) has its own system because it has a different links database to Google. I have seen references from a couple of years ago to "Page Score" but can't find it displayed anywhere now. But they will have their own metric, even if it isn't available in toolbars.

That wasn't my interpretation of what I listened to about over-optimization, but maybe you are right and we will find out soon enough anyway

Yes but then when I read of online content on this I found that Google is after sites that have high backlinks count.

I mean what I am sharing is still guess work by experts but like from where you are being linked semantically from a page would also be count. Say for example in blogs you have <div id="comments"> for comments section of the blog and links from that part of the page may not be as valueable as inside div of post.

Another report suggested that Google would devalue the backlinks factor and increase the influence of +1 factors in ranking algorithm but I doubted that because then Google would become yet another Digg

Few other reports commented on the linking factors as option to deal with over optimization and so thinking over it I realized that only way to over optimize my site's content is by stuffing keywords into the page and that is very well taken care by Google and so the over optimization part has to deal with off page SEO factors and so this is my interpretation of over optimization.

The difficulty here is that what we have isn't an official statement from Google, but something that was said by Matt Cutts in answer to a question, recorded, and subsequently published.
I haven't seen any clarifications from him appear anywhere since, and naturally there is going to be all kinds of speculation as to what will actually happen.
Interestingly, although as you say Google has covered the keyword stuffing issue, he made reference to it in his answer, saying (with reference to those that abuse SEO) "like too many keywords on a page".
Also of course he made reference to "or exchange way too many links" but I thought that was meant to have covered already as well. So I don't see this statement as a policy change but rather as an enforcement of those guidelines which already exist, with perhaps some tightening of them as well. Google has advised against "excessive" link exchanges for a long time but the fact is that there are still very many sites who are doing well and have dozens of link pages containing hundreds of links to anyone who will exchange with them.
Likewise in another thread I gave an example of keyword stuffing on my own site (which I have now addressed ) which until now had not been penalized but perhaps could be with this coming update.
To me this is rather like when the police clamp down on a particular crime in an area. The law against it and the penalties are already in place, but it has grown to the extent where they feel the need to devote extra resources to combat it.

Yes what you are saying is correct but then they way it was implemented is being played around and so they will have more better way to get those stuff removed as well and so Matt cutt is making such statements.

It could be that if he makes such statements people would anyway undo things and that could be trigger to find more clues to over optimize sites because Google has never released what they would do but has always things that they have done.

I must admit I did wonder if he just said it so that people would undo things anyway, without Google actually having to do anything
As you say it is unusual for them to advise in advance what they are going to do, but if it is true then I guess they would rather webmasters cleaned up their sites than Google having to penalize them, so in this instance perhaps it makes sense.

Link juice is the quantity of link benefits as in traffic and ranking one gains and page rank juice is the end result of such links. But link juice is related to over optimization which is gonna get stopped in few days.